A new mastoparan-like peptide has been isolated from yellow jacket (Vespula maculifrons) venom. Immunoreactive mastoparan has been observed in rat brain and human urine. Mastoparan binds strongly to mamalian membranes. Immuno-reactive ranatension has been detected in rat brain by immunocytochemistry and by radioimmunoassay. Intraventricularly injected ranatensin delays the onset of morphine or met-enkephalin catatonbia in the rat. The stimulant in wasp (Polistes annularis) venon of the adenylate cyclase of neuroblastoma-glioma hybrid cell membranes has been isolated. It is adenosine, a previously known stimulant. More Gila monster peptide has been isolated and the end-groups identified. There is a high correlation (and some notable exceptions) with the ability of polypeptides to lyse liposomes and release histamine from rat mast cells.